The present invention relates to a method for the routing of a packet of data in a digital transmission network. It can be applied notably to equipment for the shuffling arid switching of digital data comprising a network working in Asynchronous Transfer Mode (ATM). This mode of asynchronous transmission has been adopted by the CCITT (Consultative Committee International Telegraph and Telephone) for large-band integrated services digital networks more widely known by the abbreviation of LB-ISDN. More generally, the invention can be applied to all networks for the transmission of digital data elements where it is necessary to identify and route these data elements.
In a network working in ATM mode for example, the digitized information elements are exchanged among the nodes of the network in the form of packets of bits with a fixed format called "cells", a bit being a binary element taking a value of 0 or 1. A cell is formed by a header that can be used to identify the cell and notably the communication to which it belongs and an information field containing the useful data elements to be conveyed. The role of the shuffling and switching elements forming the nodes of the network is to route the cells arriving at their inlets towards one or more of their outlets. To this end, it is necessary notably to analyze the header of each incoming cell so as to deduce therefrom, firstly, the header that the cell will have when it goes out and, secondly, the outgoing direction or directions to be taken. The cells entering or going out of the nodes are conveyed by virtual paths. These paths are called virtual because they may in fact be supported by a same physical transmission line, an optical fiber or coaxial cable line for example. These paths are themselves subdivided into virtual channels. Each of the paths liable to enter or leave a node is referenced by identification numbers called VPI (virtual path identifier) for the paths and VCI (virtual channel identifier) for the channels. In general, the VPIs and VCIs may take a large number of values owing to the large number of paths and channels possible, typically several hundreds of thousands. This is especially so in networks working in ATM mode. It causes drawbacks, notably as regards memory capacities and their rates of use. Indeed, for a given node of the network, the management of all these paths, channels and associated identifiers calls for the use of random-access memories having very great memory capacities. Now, during operation, it is highly improbable that all the possible combinations of VPIs and VCIs would have to be used: this means that there is a very marked degree of under-utilization of the reserved memory.